This invention relates to a projector for projecting an optical image on a screen.
A projector is known as a means for projecting an optical image formed in accordance with a video signal on an image panel, e.g., a liquid crystal panel, with illumination light and projecting the optical image projected by the illumination light on a screen via a projection lens.
FIG. 11 shows an illuminating optical system used in a known projector. A randomly polarized light irradiated from a light source 101 as well as a light reflected by a reflection surface 102a of a parabolic mirror 102 which is a partial surface including a pole of a paraboloid of revolution have light components in an unnecessary wavelength area removed by an IR-UV filter 103. The light having the light components in the unnecessary wavelength area is separated into a plurality of beams by a first lens array 104.
A plurality of beams split by the first lens array 104 are split by a polarized beam splitter 105 into beams 106 of first linearly polarized light components and beams 107 of second linearly polarized light components, the axes of polarization of the first and second linearly polarized light components being normal to each other.
On an emergence surface of a second lens array 108 where light sources formed by the beams 107 of the second linearly polarized light components, among light sources formed on the second lens array 108 by the first lens array 104, half-wave plates 109 are mounted to convert the axes of polarization of the second linearly polarized light components of the beams 107 into those of the first linearly polarized light components, thereby aligning the axes of polarization of all small light sources.
Thus, if the linearly polarized illumination light issued from the illuminating optical system is projected on an optical image on the liquid crystal panel formed in accordance with a video signal and the optical image illuminated by the illumination light is enlargedly projected onto the screen, a large image can be displayed.
However, such a projector needs to improve the reflectivity of the beams 107 in order to ensure a highly efficient utilization of light. Accordingly, coating of silver (Ag), aluminum (Al), or the like needs to be applied to the reflection surface 105b. This is one of factors hindering the reduction of operation steps in manufacturing the projector.
Further, the right angle prism of the polarized beam splitter 105 weighs about 700 g. This is one of factors hindering the projector from being made more lightweight.